V/STOL heavier-than-air aircraft are known from GB 951 186 and GB 2 321 227 are fitted with lift-generating devices using the lift-generating effect obtained by blowing the majority of an air flow produced by an air flow generator over deflecting surfaces that are lift-generating aerofoils, linked to a load-bearing structure of the device, and therefore also of the heavier-than-air aircraft, the device comprising two longitudinal deflecting surfaces or pluralities of surfaces, arranged on either side of the roll axis of the device and extending substantially parallel with the roll axis of the device, the two longitudinal deflecting surfaces or pluralities of surfaces being symmetrical with one another with respect to the plane defined by the roll and yaw axes of the device. In this manner, the force of resistance to forward movement (aerodynamic drag) of these longitudinal aerofoils is minimized when the device moves horizontally in the direction of its roll axis, which is its main axis, i.e. in cruising flight.
WO 2011/067527 proposes a lift-generating device of this type, with the aim of providing an improved transportation capacity for an equivalent engine power, with respect to heavier-than-air aircraft with faired propellers, a capacity for generating a significant lift by maximizing the blown air flow with respect to the size and weight of the load-bearing structure, and a small penalty on the translation drag in flight or horizontal cruising flight (flight in aeroplane mode) taking account of the arrangement of the device proposed in this patent document.
Moreover, this device makes it possible to ensure that a heavier-than-air aircraft fitted therewith has excellent stability in vertical flight and in the transition phase between vertical flight and cruising flight, due to the fact that the centres of lift of the lateral aerofoils are spaced as far apart as possible within the limits of the aircraft, thus making it possible to have a powerful roll righting moment, but also a powerful pitch righting moment, as the aerofoils extend over the majority of the length of the aircraft, i.e. over more than 50% to 100% of this length. In addition, the centre of gravity of the heavier-than-air aircraft can easily be situated below the centres of lift of the longitudinal aerofoils and between said centres of lift, when the engine or engines and the cabin of the heavier-than-air aircraft are placed below the wing plane, defined by the longitudinal aerofoils and/or additional transverse aerofoils, if applicable, which provide the lift in cruising flight.
To this end, the proposed device uses aerofoils, preferably, but not necessarily, with high lift, and known as super high-lift aerofoils, subject to at least one air flow generated by at least one large-diameter fan, and therefore in this way has blown wings, and arranged so that said aerofoils provide a resistance to forward motion that is very low when the heavier-than-air aircraft is in horizontal cruising flight. With respect to the air flow generator of the device, according to WO 2011/067527, it can comprise at least one fan mounted in the load-bearing structure and centred on the roll axis, and preferably two fans spaced along said roll axis, including at least one radial fan, with an axis substantially parallel with the yaw axis, preferably arranged towards the front of said structure, or an axial fan, also with an axis substantially parallel with the yaw axis but which can be inclined by an angle of less than 30° to the yaw axis, preferably placed towards the rear of the structure, each fan drawing air through a feed opening arranged in the upper face of the structure, and the outlet air flow from each fan being distributed essentially to lateral blow vents on the longitudinal aerofoils and arranged in the sides of the load-bearing structure via radially disposed channels over at least a portion of their extent, and separated from one another by partitions for channeling the air flow which have generatrices parallel with the yaw axis.
Whether the fan is radial, with blades inclined rearwards with respect to the direction of rotation of the fan, and each pivotable and controlled in rotation about an axis substantially parallel with the axis of rotation of the fan, the blades being associated with a fixed diffuser with vanes, each vane of which is also pivotable and the orientation of which is controlled about a pivot axis parallel with that of the fan blades, or whether the fan is of an axial type, the configuration according to which the outlet flows of the fans are distributed by channels with vertical walls arranged in the load-bearing structure and laterally curved so as to open out laterally via blow vents in the longitudinal aerofoils, with a radial arrangement of the partitions delimiting the channels in order to channel the air flow leaving a fan, is not an optimal configuration either from the point of view of the space requirement, and therefore the aerodynamic drag, or for the pressure losses, and therefore for the propulsive efficiency, in particular for an axial fan that must generate a significant air flow that is discharged laterally over the longitudinal aerofoils. Flaps, optionally arranged in grids, and inclined about axes parallel with the roll or yaw axis, and arranged in lateral vents, make it possible to set the angle of attack of the blown aerofoils and/or to give the blown air flow a longitudinal velocity component. But this activated air flow, at the outlet of a radial fan, having a substantially radial velocity, and guided by channels with vertical walls, is in no way guided, inside the volume of the load-bearing structure, by these flaps in such a way as to adopt a lateral orientation, and even less so starting from an outlet flow of an axial fan having a circumferential rotational velocity component.
A VTOL heavier-than-air aircraft is also known from WO 92/01603 or U.S. Pat. No. 5,407,150 that has a lift generator using downward direction of substantially radial jets, optionally inclined downward at the outlet of a single fan mounted in the centre of the fuselage, so as to exert an upward thrust by reaction on the structure of the heavier-than-air aircraft, by means of ducts for channeling the jets, which are angled outwards and downwards so that the air leaving the downstream end of each duct is in a jet having substantially the same cross-section as the duct at its downstream end.
As an alternative, two fans are installed symmetrically to one another in the two wings of the heavier-than-air aircraft and are through-mounted fans with annular jets, which pass through the corresponding wing from top to bottom, being provided with channels by means of annular partitions that are slightly downwardly divergent. The generatrices of the deflecting surfaces are, at least at the start, either perpendicular to the radius, with respect to the axis of rotation of the fan in question, or have a non-specified orientation, but which can only be substantially perpendicular to the radius or substantially tangential, optionally in association with the downward outlet vents in a generally angular form, each of the two sides of which is both inclined very substantially on the roll axis and the pitch axis. In all cases, the air flow, which originates from a single-stage fan, is not “rectified”, that is to say not oriented substantially parallel with the axis of rotation of the fan, and therefore has a circumferential rotational velocity component, as in any flow behind a single propeller. This patent document does not propose any air flow outlet vent that is elongated and parallel with the roll axis.
In order to provide attitude control, concentric deflecting partitions can be arranged to deflect fractions of the lift-generating flow in particular directions, that may be opposite at different times, but these partitions together do not share one half of the lift-generating flow originating vertically from the fan or fans on the same side of the roll axis of the heavier-than-air aircraft. Moreover, the whole surface of the central portion of the load-bearing structure, forming the fuselage as well as the wings, cannot be used optimally, as a result of the unsuitable choice of air outlets that are distributed circularly, or hexagonally, or “in a square” which does not make it possible to ensure the longitudinal or even traverse continuity of a space reserved for the payload. In addition, in the configuration for the transition from vertical flight to cruising flight, the aerodynamics of the central portion of the load-bearing structure (wing and/or fuselage) is adversely affected by the presence of air flow outlets (see FIGS. 6, 7 and 8), which means that, during this phase, the lift is provided by the thrust of the fan and the lift of the outer portion of the wings, outside the area of influence of the fan outlet, therefore the central and enlarged portion of the load-bearing structure does not contribute to satisfactory aerodynamics in this configuration. Nor does this central portion contribute substantially when the aircraft is in the cruising flight situation, since a speed has necessarily been reached in which the lift of the external wings is sufficient to bear the aircraft. The central portion therefore serves no useful purpose in this phase either, and it even constitutes a source of aerodynamic losses that is significant at high speed.